The present invention relates to an apparatus for effecting measurement of the roundness of a workpiece, and more particularly to an apparatus for effecting the measurement of the roundness of a workpiece with various arithmetic means.
It is known that an output signal representative of the roundness of a workpiece inevitably contains a run-out signal component due to the eccentric center of the workpiece and to the positional error of the detector caused by machine vibrations. This results in inaccurate measurement of the roundness of the workpiece. Generally it is known that the signal representative of the run-out or eccentricity of the workpiece is of low frequency while the signal representative of the roundness error is of high frequency.
Certain techniques are already known for eliminating the run-out signal of the workpiece. According to one such prior technique, a high-pass filter is provided through which passes only the high frequency roundness error signal. However, the use of the high-pass filter is disadvantageous in that wave distortion occurs, in passing the filter, when the signal is at negative voltage. This seriously affects the signal representative of the roundness error of the workpiece, so that it is impossible to more accurately effect measurement of the workpiece roundness.